Method of sealing dummy bar heads in continuous casting machines

ABSTRACT

The method of sealing the gap between the walls of a mold cavity and a preheated dummy bar head in a continuous casting machine in which the gap is sealed by a highly refractory, quick setting, pasty mixture of quartz sand and water glass which is pressed into the gap whereby the said mixture is set rapidly by the heat of the dummy bar.

United States Patent Bauer et al. Jan. 21, 1975 METHOD OF SEALING DUMMY BAR [56] References Cited HEADS IN CONTINUOUS CASTING FOREIGN PATENTS OR APPLICATIONS MACIHNES 1,474,629 2/1967 France 164/274 [75] Inventors: Karl-Heinz Bauer, Dillingen, Saar; 1,959,104 5/1971 Germany 164/274 Manfred Weiler, Huettersdorf, Saar, both of Germany Primary Examiner-R. Spencer Annear [73] Assignee: Concast AG, Zurich, Switzerland Attorney Agent Flrm-Nlcho] Sandoe 22 Fl (1: l 24, 1973 1 y 57 ABSTRACT [21] Appl' 382270 The method of sealing the gap between the walls of a Related US. Application Data mold cavity and a preheated dummy bar head in a [63] Continuation-impart of Ser. No. 206,545, Dec. 9, continuous casting machine in which the p is Sealed 1971, abandoned. by a highly refractory, quick setting, pasty mixture of quartz sand and water glass which is pressed into the [52] US. Cl 164/82, 164/274, 164/137 gap whereby the said mixture is set rapidly by the heat [51] Int. Cl 322d 11/08 of the dummy bar. [58] Field of Search 164/82, 137, 274, l 3 Claims, 1 Drawing Figure Y s E Q s 4 \I Q \i 3 Q 4 Q Q s:

METHOD OF SEALING DUMMY BAR HEADS IN CONTINUOUS CASTING MACHINES This application is a continuation-in-part of application Ser. No. 206,545, filed Dec. 9, l97lnow abandoned.

The present invention relates to methods of sealing the gap between the walls of an open-ended mold cavity and a dummy bar head in the continuous casting of metal utilizing a highly refractory sealing mixture.

In the continuous casting of metal, the exit end of the mold cavity is plugged by a dummy bar head before the pouring of metal begins. The cross-section of the dummy bar head has to be somewhat smaller than the cross-section of the mold cavity to facilitate its introduction into the mold cavity. This creates a gap be tween the walls of the mold cavity and the dummy bar head.

It is known in the art to seal this gap with asbestos ropes. These ropes have to be placed into the gap, sometimes in several layers, and have to be tightly packed and pressed down, which requires considerable time. The time required for the preparation of a casting machine for casting, which includes the sealing of the dummy bar head, should be kept as short as possible. This is particularly important for casting machines whose casting cycle is exactly synchronized with the tapping cycle of the steel producing furnaces. The asbestos ropes also do not completely disintegrate when they come in contact with the molten metal, which is being poured into the mold. This is a big disadvantage since the remaining parts of the asbestos ropes are in the form of strings and are withdrawn from the mold together with the casting. These strings become then frequently entangled with components of the guide apron, i.e., rollers, which are located down-stream of the mold. The strings thereby disturb the secondary cooling of the casting by changing the spray pattern of the spray jets for the casting cooling water, which are located between the rollers. This results in an irregular cooling of the strand, which is highly undesirable, since it produces castings of poor quality. Furthermore, asbestos particles may enter into the piping system of the secondary cooling water circuit and may thereby clog up the spray jets, which also results in an irregular cooling of the casting.

It is also known to seal the gap with a metallic powder or granulated metallic material. However, on contact with the molten metal which is poured into the mold, the sealing material fuses with the molten metal and forms relatively large agglomerates, which scratch the mold walls when the casting is withdrawn.

It was further proposed to press a refractory mixture into the gap by compressed air. However, a refractory mixture suitable for such a process must have special properties, such as a certain minimum refractoriness, quick solidification, etc.

It is an object of the present invention to seal the gap between the walls of the mold cavity and the dummy bar head with a highly refractory mixture which can be applied in a quick and simple way, and which does not damage the mold walls or disturb the secondary cooling of the casting.

According to the present invention, this object is achieved by the use of a highly refractory mixture which consists of quartz sand and water glass.

It is important that this mixture is plastic, easy to spread, and solidifies quickly when in contact with air.

For these reasons, commercial grade water glass, which is sodium silicate dissolved in water, is particularly suitable as a binding material. The quartz sand should contain about percent to percent SiO and should further contain about 20 percent fines and about 50 percent grain between 0.1 and 0.3 mm, as well as about 15 percent of each of the grain size ranges 0.02 to 0.1 mm and 0.3 to 1.0 mm. Experience has shown that one part by volume of water glass should be mixed with about 1.4 to 2.4 parts by volume of quartz sand.

The accompanying drawing is a vertical cross section through a conventional mold and dummy bar head showing the manner in which the gap between the mold cavity and the dummy bar head may be sealed according to the present invention.

Referring to the drawing, the mold l is shown with the dummy bar head 2 inserted into the mold cavity 3 in the position which it would occupy at the beginning of a continuous casting operation.

The continuous casting of a steel slab has been selected to further explain the present invention. The dummy bar head 2 is preheated as usual by gas jets to a surface temperature of over C. and is then mounted on the dummy bar and inserted into the mold cavity 3. For a slab cross-section of 1550 X 250 mm, a gap of about 6 mm width will form all around the circumference of the mold cavity walls between the dummy bar head and the mold cavity walls. The width of the gap can vary, since the mold cavity walls could have a conical shape so that the gap width depends on how high the dummy bar head has been pushed upwards into the mold cavity.

Prior to moving the dummy bar head into the mold cavity, a highly refractory mixture was prepared by adding about 3 parts of quartz sand to about two parts of water glass, while constantly stirring the mixture. The sand was added gradually, while constantly stirring, until the mixture became pasty. This mixture was filled into an airtight conventional pressure vessel, with an inlet pipe for compressed air leading into its upper part. The pressure vessel may be mounted on wheels. One end of a hose leads from the bottom part of the pressure vessel into a pipe 5, which is provided with a stopcock. The apparatus is brought to the mold, the stopcock is opened, and the compressed air presses the mixture 4 from the pressure vessel via hose and pipe, as indicated by arrow 6, into the gap. Only one layer of the mixture has to be applied. The mixture sets or binds in about 20 seconds, which is aided by the temperature of the preheated dummy bar head. The whole process of sealing a dummy bar head for slabs can therefore be easily accomplished within one minute. Thereafter, metal chips and scrap are deposited upon the dummy bar head in the customary manner, to guarantee a rapid fusion between the molten metal which is then poured into the mold and the strand connection parts of the dummy bar head, i.e., rail sections. The withdrawal of the strand is started as soon as the level of the molten metal in the mold has reached a certain level, which is usually about 10-15 cm below the upper edge of the mold.

Other binding materials, such as aluminum mono phosphate, can be used instead of water glass. The important requirements are that the mixture solidifies very quickly and prevents the penetration of liquid metal into the gap until the liquid metal which is in contact with the mixture has solidified.

2. The method according to claim 1 in which said quartz sand contains about percent to percent SiO and contains about 20 percent fines and about 50 percent grains between 0.1 and 0.3 mm.

3. The method of claim 1 in which the dummy bar head is preheated to a temperature of at least C. prior to inserting into the mold whereby the mixture is set rapidly by the heat of the dummy bar head. 

1. The method of sealing the gap between the walls of a mold cavity and the dummy bar head prior to pouring molten metal into the mold cavity which comprises, inserting the dummy bar head into the mold cavity, and pressing into tHe gap between the walls of the cavity and the dummy bar head a pasty mixture of quartz sand and water glass comprising one part by volume of water glass and from 1.4 to 2.4 parts by volume of quartz sand.
 2. The method according to claim 1 in which said quartz sand contains about 90 percent to 95 percent SiO2 and contains about 20 percent fines and about 50 percent grains between 0.1 and 0.3 mm.
 3. The method of claim 1 in which the dummy bar head is preheated to a temperature of at least 100*C. prior to inserting into the mold whereby the mixture is set rapidly by the heat of the dummy bar head. 